1. Field of the Invention
The present invention relates generally to a silicone connector for testing a semiconductor package. More particularly, it concerns the use therein of a low-density conductive silicone member that is subject to wear or damage from pressure applied by a solder ball of the semiconductor package.
2. Description of the Related Art
A manufactured semiconductor packages undergoes various tests to ensure its reliability. Generally, there are two kinds of package tests: electrical characteristic and burn-in tests. The electric characteristic test examines the behavior and connection of a package under test by connecting all of its input/output (I/O) signal terminals to test-signal generating circuits under normal operating conditions. The burn-in test examines the endurance of the package under test by connecting some of its I/O signal terminals to test-signal generating circuits and stressing the package at elevated temperature and voltage.
In both tests, a connector is utilized for supporting a semiconductor package to make electrical and mechanical contact with the package, the connector acting as a medium to connect external interface terminals of the package with a test substrate. The shape of the connector usually depends upon the type of the semiconductor package.
For a ball grid array (BGA) type package having solder balls as external interface terminals, the connector has probe needles embedded in a plastic body, as disclosed in Korean Utility Model Gazette Nos. 182523 (Mar. 7, 2000) and 247732 (Sep. 11, 2001). Spring-loaded, so-called “pogo” pins are commonly utilized as the probe needles.
More and more finely pitched (linearly spaced, typically expressed in pins/centimeter) pogo pins of the connector are needed to test thinner and smaller semiconductor packages having more and more finely pitched solder balls, such as chip scale packages (CSP) and wafer level chip scale packages (WLCSP). However, the pitch of pogo pins cannot become finer without limit. Pogo pins may cause damage to the solder balls during the at least two-step test process, thereby increasing the occurrences of deformation defects in packages. Shortening the length of the pogo pins is necessary to cope with ultrahigh test signal frequencies, but it is difficult to manufacture the pogo pins that are less than or equal to 3 mm long.
To reduce damage to the solder balls of a semiconductor package for ultrahigh test signal frequencies, a silicone connector 100, as shown in FIGS. 1 to 3, is utilized. The conventional silicone connector 100 is a connector for testing semiconductor packages, which is made by solidifying insulating silicone powder 25 and conductive powder 35. The silicone connector 100 comprises a connector body 20 and a low-density conductive silicone member 30. The connector body 20 is made of the solidified insulating silicone powder 25. The low-density conductive silicone member 30 is made by bringing the conductive powder 35 to a site of the connector body 20 corresponding to a solder ball of a semiconductor package under test. The silicone member 30 is positioned and oriented to be perpendicular to the connector body 20, like a pillar, as shown.
The lower surface 31 of the low-density conductive silicone member 30 is exposed from the lower surface 21 of the connector body 20. The lower surface 21 contacts with a substrate pad of a test substrate (91 in FIG. 4) to form an electrical connection. The upper surface 33 of the low-density conductive silicone member 30 is exposed from the upper surface 23 of the connector body 20, and contacts with a solder ball of the semiconductor package under test (81 in FIG. 4) to form an electrical connection.
The conventional silicone connector 100 typically is manufactured as follows. First, the insulating silicone powder 25 and the conductive powder 35 are mixed at a predefined ratio and are melted in a mold frame. Second, the conductive powder 35 is brought to a site where the low-density conductive silicone member 30 will be formed, as illustrated schematically in FIG. 3. Specifically, electric power applied selectively to the site where the low-density conductive silicone member 30 will be formed brings the conductive powder 35 contained in the melted silicone mixture to the formation site. Third, the conventional silicone connector 100 is completed by solidifying the melted silicone mixture.
How the conventional silicone connector 100 contacts with the semiconductor package 80 is explained with reference to FIG. 4 as follows. First, a test substrate 90 having the silicone connector 100 installed thereon is prepared. The lower surface 31 of the low-density conductive silicone member 30, exposed from the lower surface 21 of the connector body 20, contacts with a substrate pad 91 of the test substrate 90 to form an electrical connection.
Next, a solder ball 81 of the semiconductor package 80, located above the upper surface 23 of the silicone connector body 20, applies a designated force on the upper surface 33 of the low-density conductive silicone member 30, producing an elastic contact therewith to form an electrical connection. Finally, package tests are conducted by flowing test signals from the test substrate 90 to the semiconductor package 80 via the silicone connector 100.
Because the silicone connector 100 including the low-density conductive silicone member 30 is made of relatively soft and elastic materials, the force applied by the solder ball 81 of the semiconductor package 80 tends to depress the upper surface 33 of the low-density conductive silicone member 30 so as to enclose a periphery of the solder ball 81 in a slight recess, as shown. This slight interference fit and resulting soft-material deformation is desirable, as it produces a robust electrical connection. The low-density conductive silicone member 30 bulges out slightly in the middle, and the lower and upper surfaces 21 and 23 of the connector body 20 enclosing the low-density conductive silicone member 30 also bulge slightly, as shown, respectively down and up.
Undesirably, however, the low-density conductive silicone member 30 is relatively soft and thus is susceptible to wear or damage caused by repeated contact with the solder ball 81 of the semiconductor package 80. This is because over its useful life the silicone connector 100 has repeatedly to contract and expand in contact with successive ones of the semiconductor package 80 being tested. A defect can develop from hollows or voids or pits at the upper surface 33 of the low-density conductive silicone member 30 caused by the repeated pressure from the solder ball 81. Consequently, the conventional silicone connector 100 has to be replaced frequently due to wear and ultimate test failure-prone damage to the low-density conductive silicone members 30. Higher test costs are incurred.
To solve this problem, a silicone connector having a metal ring at the upper end of a low-density conductive silicone member is disclosed in Korean Utility Model Gazette No. 278989. The metal ring interposed at the upper end of the low-density conductive silicone member tends to prevent hollows at the upper ends of the low-density conductive silicone member caused by the repeated pressure of the solder ball thereon. The metal ring accordingly may help lengthen the life span of the silicone connector.
Unfortunately, the low-density conductive silicone member is relatively soft, and the proposed metal ring is relatively hard. Thus another problem arises with use of the proposed metal ring: The metal ring can detach from the upper end of the low-density conductive silicone member due to the repeated deformation and restoration of the shape of the silicone connector caused by the repeated contact with the solder balls of the semiconductor package under test.
Another silicone connector having a metal plate at the upper end of a low-density conductive silicone member is disclosed in Korean Utility Model Gazette No. 312739. The metal plate might protect the low-density conductive silicone member, and the metal plate might thereby help lengthen the life span of the silicone connector.
Unfortunately, the proposed metal plate completely covers the upper end of the corresponding low-density conductive silicone member. Moreover, the metal plate is relatively hard. Finally, the metal plate provides an inherently less stable and reliable electrical contact with a solder ball than does the relatively soft low-density conductive silicone member.
The contacting pressure can be increased for stable electrical contact between the metal plate and the solder ball of the semiconductor package. But the increased pressure can cause damage to the low-density conductive silicone member, thereby generating a recurring problem of significantly reduced elasticity. Specifically, an undamaged silicone connector returns back to its initial state owing to its own elasticity, i.e. it is shape-retentive. However, the repeated increased pressure applied by the metal plate may accelerate damage to the low-density conductive silicone member, and a damaged silicone connector does not reliably return to its initial state, i.e. it is permanently deformed and thus damaged and test failure-prone.
In addition, the metal plate requires extra manufacturing steps such as plating, etching, and coating, leading to a more complex and costly manufacturing process.
Finally, a big difference between the coefficients of elasticity of the metal plate and the low-density conductive silicone member can cause a delamination phenomenon at their interfacing surface, thereby leading to a serious failure mode in which the metal plate detaches from the upper end of the low-density conductive silicone member.
Accordingly, the present invention is to provide, among other things, a silicone connector that may protect the low-density conductive silicone member having good junction properties, forming robust electrical and mechanical contact, and using existing connector-manufacturing methods.